125 lines
3.2 KiB
C++
125 lines
3.2 KiB
C++
/*
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Bullet Continuous Collision Detection and Physics Library
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Copyright (c) 2003-2006 Erwin Coumans http://continuousphysics.com/Bullet/
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This software is provided 'as-is', without any express or implied warranty.
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In no event will the authors be held liable for any damages arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it freely,
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subject to the following restrictions:
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1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
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2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
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3. This notice may not be removed or altered from any source distribution.
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*/
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#ifndef UNION_FIND_H
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#define UNION_FIND_H
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#include "LinearMath/btAlignedObjectArray.h"
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#define USE_PATH_COMPRESSION 1
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struct btElement
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{
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int m_id;
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int m_sz;
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};
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///UnionFind calculates connected subsets
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// Implements weighted Quick Union with path compression
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// optimization: could use short ints instead of ints (halving memory, would limit the number of rigid bodies to 64k, sounds reasonable)
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class btUnionFind
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{
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private:
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btAlignedObjectArray<btElement> m_elements;
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public:
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btUnionFind();
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~btUnionFind();
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//this is a special operation, destroying the content of btUnionFind.
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//it sorts the elements, based on island id, in order to make it easy to iterate over islands
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void sortIslands();
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void reset(int N);
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inline int getNumElements() const
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{
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return int(m_elements.size());
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}
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inline bool isRoot(int x) const
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{
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return (x == m_elements[x].m_id);
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}
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btElement& getElement(int index)
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{
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return m_elements[index];
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}
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const btElement& getElement(int index) const
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{
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return m_elements[index];
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}
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void allocate(int N);
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void Free();
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int find(int p, int q)
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{
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return (find(p) == find(q));
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}
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void unite(int p, int q)
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{
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int i = find(p), j = find(q);
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if (i == j)
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return;
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#ifndef USE_PATH_COMPRESSION
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//weighted quick union, this keeps the 'trees' balanced, and keeps performance of unite O( log(n) )
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if (m_elements[i].m_sz < m_elements[j].m_sz)
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{
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m_elements[i].m_id = j; m_elements[j].m_sz += m_elements[i].m_sz;
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}
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else
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{
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m_elements[j].m_id = i; m_elements[i].m_sz += m_elements[j].m_sz;
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}
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#else
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m_elements[i].m_id = j; m_elements[j].m_sz += m_elements[i].m_sz;
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#endif //USE_PATH_COMPRESSION
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}
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int find(int x)
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{
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//assert(x < m_N);
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//assert(x >= 0);
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while (x != m_elements[x].m_id)
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{
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//not really a reason not to use path compression, and it flattens the trees/improves find performance dramatically
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#ifdef USE_PATH_COMPRESSION
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//
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m_elements[x].m_id = m_elements[m_elements[x].m_id].m_id;
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#endif //
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x = m_elements[x].m_id;
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//assert(x < m_N);
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//assert(x >= 0);
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}
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return x;
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}
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};
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#endif //UNION_FIND_H
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